Multi-band antenna formed of closely spaced folded dipoles of increasing length



Jan. 26, 1965 E R 3,167,775 1 MULTI--BAND ANTENNA FORMED 0F CLOSE-LY SPACED FOLDED DIPOLES OF INCREASING LENGTH 2 Sheets-Sheet 1 Filed Sept. 29, 196D INVE'NTOR RUDOLF- GUER'FLER ATTORNEYS Jan. 26, 1965 R. GUERTLER 3,167,775 7 MULTI--BAND ANTENNA FORMED OF CLOSELY SPACED FOLDED DIPOLES 0F INCREASING LENGTH 2 Sheets-Sheet 2 Filed Sept. 29, 1960 z \NVENTOR RUDOLF- GUERTLER ATTORN EyS Want WZWZM/LV I MULTI-BAND ANTENNA FORMED F CLOSELY United States PatentQ This invention relates to antennas, and particularly it 7 waves on the feeder.

A still further object of the invention is to provide an antenna of sturdy construction, low wind resistance and easy mounting.

The invention provides an antenna consisting of a plurality of dipoles having parallel axes disposed in 'a common plane with the centers of the dipoles defining a straight line, the spacing between adjacent dipoles being less than one-tenth of a wavelength at the highest operating frequency, the length of the dipoles increasing from pair to pair, and all dipole elements on one side of said straight line being serially connected thus forming a meandering conducting path, the dipole elements on the other side of said straight line being similarly connected and the terminals of the last longest dipole being short circuited whereby a single continuous conducting path is formed leading from one input terminal of the antenna through all dipole elements to the other input terminal of the antenna.

The series connection of all dipole elements on each side enables the elements to operate simultaneously in two electromagnetic modes-firstly in a radiating or antenna mode,'andsecondly in an essentially non-radiating transmission line mode. The combination and control of the radiating mode and the transmission line mode on the serially connected dipole elements'make it possible to obtain'high directivity, high gain, favourable radiation patterns and a useful feed point impedance over a wide frequency. range or over several distinct frequency bands.

The objective of obtaining high directivity, high gain and.

a useful feed point impedance requires that the length of the shortest dipoles be approximately equal to a hal wavelength at the highest operating frequency, so that the transmission line stub consisting of adjacent elements of the shortest dipole pair is about a quarter-wave long and has a high input impedance.

An antenna according to the invention may mechanically consist of several parts connected conductively to form a meandering conductive path, or may consist of a single wire orrod bent to form a meandering path in accordance. with the invention.

stood by reference to the following description taken in connection with the accompanying drawings, in which FIG. 1 shows schematically the fundamental type of an antenna acording to the invention.

FIGS. 2 and 3 show derivatives of the antenna of FIG. 1, when the last longest dipole is open circuited at the center or removed. I a

FIGURE 4' shows an antenna consisting of two pairs of The principle of the invention, its operation and advantages will best be underice dipoles serially connected according to the invention, suitable for two distinct frequency ranges of about 1:3 ratio of centre frequencies.

FIGURE 5 shows a graph of the radiation pattern in the plane of the antenna in the higher frequency range.

FIGURE 6 is an explanatory diagram of a conventional active three-half-wave dipole combined with a passive half-wave dipole.

FIGURE 7 is an explanatory diagram for explaining the improvements of the present invention.

FIGURE 8 shows an antenna similar to FIGURE 4 combined with a screen or reflectors.

FIG. 1 shows the fundamental type of antenna according to the invention. It consists of three pairs of dipoles with elements connected serially so that a continuous meandering conductive path is obtained between the terminals A and B, namely, A-l-S-S-7-9-11-10-8-6-4-2-B, the length of the dipoles increasing from pair to pair, 1, 2, 3, 4 being the shortest elements, 9, l0, and halves of 11 being the longest elements. M is the neutral-potential point of the antenna and may be grounded. All said dipole elements perform a double operation-as radiators, and as conductors of transmission line stubs. Elements on opposite sides of the straight line connecting centers of the dipoles, as for instance 1 and 2, or 3 and 4, or 9 and It or 11, act as dipoles. Adjacent elements as, for instance,

1-3, or 3-5, or 9 and part of 11 on the left side of M,

act as transmission line stubs. Straight elements inside the antenna belong substantially to three circuits; for instance, element 3 is part of the dipole 3-4, part of the stub 1-3, and part of the stub 3-5. The multiple operation of the antenna elements represents amultitude of adjustable antenna parameters. The frequency range, particularly, is determined by the length of dipole elements. Variation in the spacing of adjacent elements and variation of element diameters have only a small influence on the antenna mode and a limited influence on the transmission line mode.

The antenna, FIGURE 2 is derived from FIG. 1 by leaving the terminals of the last longest dipole 11, opencircuited at the center M. This variant, FIG. 2, comprises the same transmission line stubs as thefundamental antenna form of FIG. 1 from which it is obtained by opening the last longest dipole at the center M. "An antenna according to FIG. 2 has the same, radiating elements and the same transmission line stubs as an antenna of the same, 'geornetry but with short-circuited terminals M of the last longest dipole of FIG. 1. It has similar qualities to the fundamental antenna with some quantitative variations as, e.g.,changed frequency bands.

The antenna, FIG. 3, can be derived from FIGUREI by removing element ll. The variant of FIG. 3 has one radiating dipole and two transmission line stubs less than the corresponding fundamental antenna of FIG. 1-, from I which it is derived. Due to the remaining configuration similar in principle to FIG. 1, the variant of FIG. 3 exhibits similar qualities to the fundamental antenna,

'FIG..1.

FIGURE 4 shows an example of an antenna of type FIGURE 1. The antenna consists of straight tubular conductors, 1, 2, 3, 4, 5, 6 and 7-8, joined by coupling members such as conductive strips 13, 35, 57, 63, 46, and 24, so that a meandering conductive path in accordance with the invention is obtained. The antenna can be used in two distinct frequency ranges. Excellent performance is obtained when the longer folded. dipole 5-7-8-6 represents a three-half-wave dipole at frequencies where 1-2 and 3-4 operate as half-wave dipoles. At about one-third of this frequency 5-7-8-6 operates as folded half-wave dipole.

I In an actual television receiving antenna for the frequency bands 63 to 70 megacycles and 181 to 202 megacycles of a construction similar to FIGURE 4, according to the invention, the following dimensions were used:

. Inches Length of sections 1, 2, 3, 4 13 /2 Length of sections 5 and 6 40% Length of section 7-8 82 Axial separationbetween adjacent sections, that is. between 1 and 3, between 3 and 5, and between S and.7 2/2 Total width of antenna, that is separation between axes of sections It and 7 7 /2 7 All the sections 1 to 7-8 are of aluminum tubing of /2 inch or inch outer diameter.

built also of a single rod or tubular conductor bent to the meandering form indicated by A--l3-S-786-4 2-B.'

" In the lower frequency band, part 5-786 operates like The antennacan be In the higherfrequency bandtlSl-to 202 megacyclcs) the part 5-7-8-6 operates as a folded tlneehalf-Wave dipole, and the part 1-3-4-2 as a folded half-wavedipole The radiation pattern inthe plane ofthe antenna, measured at frequencies near the centre-of the higher fre- Em, is 'greater'than the backward-maximum, Eb. The

' front-to-back ratio, Em/Eb, for an actual antenna as described above'in connection WithFlGURE 4, is. about' i 2 or more. 7 frequency of the higher frequency range (181jto 202 At frequencies near the'lowest and highest megacycles), somesmall side-lobes will appear in the radiation pattern, FIGURE 5.

I I To appreciate fully the merits of an antenna incorpo-- rating the invention, the properties; of a known antenna type indicated in FIGURE 6, maybe described. This The forward-maximum,

H on section 5, FIGURE 4. Similarly, phase reversal is obtained between strip 24 and point I on section 6. The quarter-wave stubs 1-3 and 2-4 have also to secure a phase reversal with respect to the driving voltage across A-B as at the input of the folded fthree-quarter-wave dipole 5-78t5 driving voltage of opposite polarity as required.

The theory of antennas consisting of serially connected dipole elements in accordance with theinvention has not yet been fully developed. Howevenlt is believed that distribution of radiating or antenna currents takes place approximately as indicated in FIGURE 7. Currents 12 and 34 in dipoles 1-2 and 3-4 respectively, have the same direction as currents 55,77, 66 and 88, in the outer thirds of dipoles 5%? and 7-8; currents 56 and 73 in the middle thirds of the dipoles 56:and "7-8 have the-opposite direction. Current 34 neutralizes current 56, and

current 78 acts like current in a reflector with respect to quency range consists substantially of two narrow lobes, asindicated in diagram, FIGURE 5. The forward-lobe "F has a field intensity maximum, Em, in the z direction; The backward-lobe, B in FlGURE 5,has a maximum of Pb, in direction opposite to z.

dipole 1-2.,that is the central part of the antenna acts like an endfire array, and this accounts for directivity in direction z as expressed in the radiationpattern, FIG- URES. The relativenarrowness of the -'forward-lobe and backward-lobe and the highergain are due to the-colinear arrangement of CurrentdistributionsSS and 66,

177 and 88, and the nearly co-linear end-fire arrangement of currents l2 and 73, FIGURE 7.

The input impedance'of an antenna as represented in FlGURE 4 matches satisfactorily to a feeder of 300 ohm characteristic impedancel It is {quite obvious that at lower irequenciesthe feed point impedance' will match the feeder because the antenna operates substantially. as a foldedhalf-wave dipolewith a moderate inductive loadingat the feedpointf Satisfactory matching is obtainable also in the higher frequency range.- Experiments with an antenna Whose dimensions have been given abovein connection with conventional type consists of a three-half-wave dipole n n, and an adjacent passive half-wave elementp, as

: described'by F.:A. Kolster, AntennaDesignforTelevi-' jsion and-RM; Reception,.Proceedings'of the Institute of Radio Engineers, 'volume36, pages 1242-1248;.Octoberv 1948. The current distribution indicated bymm, mn, nn,

same direction, but current mn has the'opposite direction;

The operation of an antenna, FIGURE 4, incorporatingthe invention, is considerably more involved. In the higher frequency range, the part 134 -2 represents a folded half wave dipole with element 3-4 loaded at the centre witha folded three-half-Wave dipole 5-7-86. The quarter-wave stubs 1-3 and 2-4, and the threequarter-wave stubs 5-7 and 6-8 have a broadbanding effect encountered in folded dipoles. Section 3 together wit h'the adjacent part of section 5 operate as a phasereversing quarter-wave stub, that is phase reversal takes place between strip lfi the end ofsectiofn 3-and point FIGURE 4, showed a voltage standing-wave ratio of about 1.5 at the lowest and highest frequency of the higher frequency range; :a'txthese boundary frequencies of the rangethe antenna impedance-had only a small reactive component. The-matchingxis noticeably better than with ,a conventionally tolerated standing-wave'ratio of 2-Ifor good television-reception; If an antenna is requiredfor three, frequency bands; three pairs of dipoles should be used, thatis, a configuration similar to FIG. 1.

Directivity and'gain of an antenna incorporating the invention can be improved by adding one or severalknown and 17p, shows that the currents mm, nn, and pp have the 4 'reduce the verticalacceptance -angle..

typesiofpassive elements as reflectors and/orvdirectors.

FIGURE 8 shows schematically the plan projection of an antenna according to .the invention, with: a reflector S comprising, a single: long element orv colinea'r shorter elements or a suitablescreen. All known methods of combining a plurality of 'sirnilar antennas into an array (for instance cophased arrays, colinear arrays, broadside arrays, end-fire arrays.) can be appliedto antennas according to theinvention; I

Similar antennas as, for 'in'stance, FlGURE 4 or FIG- UREB, may bestacked vertically to increase gain and to There are many other types of antennas feasible. in

accordance with the invention, and many kinds: of arrays employing antennas incorporating the invention.

I claim: 1. An antenna consisting of aplur'ality of pairs of dipoles having parallel axesdisposed in a common plane With the centers of said'di'poles defining a straight line, the spacing between adjacent dipoles being less than onetenth of a wavelength at'the highest frequency of opera tion, the length of the dipoles increasing-from pair to pair, all dipole elements on one side of; saidstraight line beingconnected serially, the. terminals of the last longest dipole being short-circuitecl, and all dipole elements on theother sideof said straight line being connected serially, so that a continuous meanderingiconducting path is provided starting from one terminal of the first shortest dipole and continuing serially through all dipole elements on one side of said straight line, thence through all dipole elements on the other side of said straight line and finishing at the other terminal of the first shortest dipole, thus enabling each element to act as a radiating element in cooperation with the element opposite with reference to said straight line and to take part in transmission line stub operation with an adjacent element, the entire antenna so formed exhibiting highest sensitivity along said straight line, and being capable of operating over a wide range of frequencies.

2. An antenna consisting of first and second pairs of dipoles, the dipoles of the second pair being longer than the dipoles of the first pair, all dipoles having parallel axes disposed in a common plane with the centers of said dipoles defining a straight line, the spacing between adjacent dipoles being less than one-tenth of a wave-' length at the highest frequency of operation, all dipole elements on one side of said straight line being connected serially, the terminals of the last longer dipole being shortcircuited, and all dipole elements on the other side of said straight line being connected serially, so that a continuous meandering conducting path is obtained starting at one terminal of the first shorter dipole in said first pair, passing serially through all dipole elements on one side of said straight line, thence through all dipole elements on the other side of said straight line and finishing at the other terminal of said first shorter dipole, thus enabling each element to act as a radiating element in 6 t cooperation with the element opposite with reference to said straight line and to take part in transmission line stub operation with an adjacent element, the entire antenna so formed exhibiting highest sensitivity along said straight line, and being capable of operating in two frequency bands.

3. An antenna according to claim 2 wherein the length of the dipoles in said second pair is approximately three times the length of the dipoles in said first pair, the dipoles operating in two distinct frequency ranges whereof the ratio of the range center frequencies is approximately 1:3 whereby the wavelengthat the center frequency of the higher frequency range is about twice the length of a dipole in said first pair and significant sensitivity at 'frequencies of the higherfrequency range being exhibited along said straight line in the direction from the longer to the shorter dipoles.

References Cited by the Examiner UNITED STATES PATENTS 2,192,532 3/40 Katzin 343908 2,242,023 5/41 Cork et a1. 343-812 2,821,710 1/58 Hale 343--806 2,875,441 2/59 McGrane 343'-806 HERMAN KARL SAALBACH, Primary Examiner.

GEORGE N. WESTBY, Examiner. 

1. AN ANTENNA CONSISTING OF A PLURALITY OF PAIRS OF DIPOLES HAVING PARALLEL AXES DISPOSED IN A COMMON PLANE WITH THE CENTERS OF SAID DIPOLES DEFINING A STRAIGHT LINE, THE SPACING BETWEEN ADJACENT POLES BEING LESS THAN ONETENTH OF A WAVELENGTH AT THE HIGHEST FREQUENCY OF OPERATION, THE LENGTH OF THE DIPOLES INCREASING FROM PAIR TO PAIR, ALL DIPOLE ELEMENTS ON ONE SIDE OF SAID STRAIGHT LINE BEING CONNECTED SERIALLY, THE TERMINALS OF THE LAST LONGEST DIPOLE BEING SHORT-CIRCUITED, AND ALL DIPOLE ELEMENTS ON THE OTHER SIDE OF SAID STRAIGHT LINE BEING CONNECTED SERIALLY, SO THAT A CONTINUOUS MEANDERING CONDUCTING PATH IS PROVIDED STARTING FROM ONE TERMINAL OF THE FIRST SHORTEST DIPOLE AND CONTINUING SERIALLY THROUGH ALL DIPOLE ELEMENTS ON ONE SIDE OF SAID STRAIGHT LINE, THENCE THROUGH ALL DIPOLE ELEMENTS ON THE OTHER SIDE OF SAID STRAIGHT LINE AND FINISHING AT THE OTHER TERMINAL OF THE FIRST SHORTEST DIPOLE, THUS ENABLING EACH ELEMENT TO ACT AS A RADIATING ELEMENT IN COOPERATION WITH THE ELEMENT OPPOSITE WITH REFERENCE TO SAID STRAIGHT LINE AND TO TAKE PART IN TRANSMISSION LINE STUB OPERATION WITH AN ADJACENT ELEMENT, THE ENTIRE ANTENNA SO FORMED EXHIBITING HIGHEST SENSITIVITY ALONG SAID STRAIGHT LINE, AND BEING CAPABLE OF OPERATING OVER A WIDE RANGE OF FREQUENCIES. 